Sink/washing machine waste to soil pipe - anti-syphon trap the trick

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Jethro 15 years ago

Following the big freeze, and having a narrow escape with a frozen waste pipe going to an outside drain, I want to re-plumb the pipe to go down the toilet stack in the cloakroom it passes, on it's way out the wall.

I know you can get 90degree pan connectors with a fitting to accept a waste pipe - so that side is sorted. However I am worried about siphonage, when the toilet is flushed.

A lot of googling (why are plumbing matters so off-grid ?) and a phone call to a local plumbers merchants suggests an anti-siphon trap

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do the job. The pipe run starts with the washing machine, and goes about 6' before it's joined by the sink waste, and then will go about 5' into the soil pipe.

Does this seem practical, sensible, and the correct way ? Presumably I will need two (although the shop guy said one on the basin - the washing machine wouldn't need one as it was so long ???????)

cheers guys.

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T

Tim Watts 15 years ago

Jethro ( snipped-for-privacy@googlemail.com) wibbled on Friday 21 January 2011 17:03:

Yes - you will get a strong suction effect when the loo is flushed, if a block of loopaper goes down (makes a most effective piston).

The trap you mentioned would be a good solution. It is likley the AAV integral to that trap will be sufficeint to protect the other trap, but I couldn't absolutely guarantee it. What's the seal depth on the other trap?

Another solution is to "roll your own" with a small AAV on a short vertical tee'd off pipe - perhaps near to the washing machine standpipe so the AAV could be put roughly as high as the top of the machine's standpipe thus abive the waterline of the basin.

A further solution would be to use a HepVO on the basin which will take care of everything.

Cheers

Tim

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Tabby 15 years ago

What an antisyphon trap does is let air into the pipework if a slight vacuum shows up. So there's not much need for 2 of them on one pipe.

I like keeping the drains as separate as they already are, that way if one ever blocks you do at least have the other.

NT

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Jethro 15 years ago

(Hits head with hand) Duh !!!! Of course ...

Well IMO the chances of the soil pipe blocking are much smaller than the chances of the waste pipe getting blocked (or frozen). And besides, the existing arrangement is aesthetically s*it ... it comes out one side of the house, and goes all the way along (under the patio door) to the otherside ... a good 5m run.

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A

A Plumber 15 years ago

(Hits head with hand) Duh !!!! Of course ...

Well IMO the chances of the soil pipe blocking are much smaller than the chances of the waste pipe getting blocked (or frozen). And besides, the existing arrangement is aesthetically s*it ... it comes out one side of the house, and goes all the way along (under the patio door) to the otherside ... a good 5m run.

Just boss the waste pipes into the soil stack, you should have 3" seal traps on as the soil stack is vent to the atmosphere, there should be no problems witht the traps being pulled. No need for ati-vac traps.

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Sink/washing machine waste to soil pipe - anti-syphon trap the trick

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